Results: A lithium-ion battery with a positive electrode made of carbon nanotubes delivers 10 times as much power as a conventional battery and can store five times as much energy as a conventional ultracapacitor.

Why it matters: Researchers have been trying to make battery electrodes from carbon nanotubes because they are highly conductive and have a large surface area, two characteristics that are important for power density and storage capacity. Lithium-ion batteries with nanotube electrodes could extend the range of electric vehicles and allow electronic gadgets, including smart phones, to work longer without recharging.

Methods: MIT scientists made dense, porous nanotube films by dipping a glass slide alternately in solutions of positively and negatively charged nanotubes. The films were then heat-treated and incorporated into a lithium-ion battery with a conventional negative electrode and electrolyte. When current was passed through the battery, lithium ions reacted with oxygen on the surface of the nanotubes. The electrodes’ porous structure improves energy density by providing a large number of reaction sites for the lithium ions, as well as an easy route in and out of the electrode.

Next steps: The researchers are developing a technique for spraying the nanotube solutions on the slide, which should speed up the process of making the films from days to hours. They have licensed the technology to an undisclosed battery company.